Prevention of Starch Degradation in Pump, Paper or Board Making Processes

ABSTRACT

The invention relates to biocidal systems comprising zinc ions and an oxidizing or non-oxidizing biocide, their use, and methods for preventing or decreasing starch degradation in starch-containing process waters from pulp, paper or board production processes.

FIELD OF THE DISCLOSURE

This application relates to biocides and more particularly to biocidalsystems comprising Zn ions and biocides, their use, and methods forpreventing or decreasing starch degradation in pulp, paper, or boardmaking processes.

BACKGROUND

It is well known in the pulp, paper or board making industry to applyoxidizing or non-oxidizing biocides to control microbial growth.Examples of commonly used non-oxidizing biocides are glutaraldehyde,2,2-dibromo-3-nitrilopropionamide (DBNPA),2-bromo-2-nitropropane-1,3-diol (Bronopol), quaternary ammoniumcompounds, carbamates, 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT),and 2-methyl-4-isothiazolin-3-one (MIT). Typical examples of commonlyused oxidizing biocides are chlorine, hypochlorite salts, hypochlorousacid, chlorinated isocyanurates, bromine, hypobromite salts, hypobromousacid, bromine chloride, chlorine dioxide, ozone, hydrogen peroxide, orperoxy compounds.

A specific application of biocides is the control of starch degradationin process waters of the paper industry. Starch is a widely usedadditive in paper making. Actually paper making is the largest non-foodusage of starch. For example, in the wet end of a paper machine, starchis used to improve paper strength. In the dry end of a paper machine,starch is used for coating the paper in a process called surface sizing.This gives paper additional strength and better printing properties.

Amylase is an enzyme that catalyzes degradation of starch. It isproduced by many microorganisms, both fungi and bacteria, and is alsopresent for example in human saliva. Amylase enzymes are divided intothree groups: α-, β- and γ-amylases. They all hydrolyse α-1,4-glycosidicbonds that link together glucose units of starch molecule. β-amylase canbreak only the second α-1,4-glycosidic bond, yielding into two glucoseunits (maltose). α-amylase can attack any bonds in the starch moleculeand thus is often faster acting than β-amylase. γ-amylase cleaves oneglucose unit at the time and is most efficient in acidic environments.

Process waters in the paper industry can contain microorganisms whichcan produce amylase enzymes that degrade starch and cause loss of thefunctionality of added starch additive. This will lead either to paperquality issues, or alternatively force to increase starch dosages thuscreating unwanted additional costs.

Current practices in controlling starch degradation have been inadequatein efficacy or have required economically unfeasible high biocidedosages. Especially when process water with high amylase activity isused for pulping of recycled fiber, or in re-pulping of dry broke of apaper or board machine, degradation of starch is easily taking place andthe benefits of the starch already included in the fibrous material fromrecycled paper (which contains plenty of starch from the originalproduction process) is lost.

WO 2012/025228 A1 discloses a method for manufacturing paper, wherein acellulosic material containing starch is treated with biocides, followedby adding an ionic polymer and an auxiliary ionic polymer, both polymershaving different average molecular weight and different ionicity.

DESCRIPTION

Surprisingly, it has been found that when combining Zn ions (e.g., via aZn ion source compound) with one or more biocides, an enhancedprevention or reduction of starch degradation can be obtained. Althoughnot intending to be bound by theory, it is believed that this is due totwo different mechanisms, one mechanism inhibiting existing amylaseactivity and the other mechanism preventing the production of newamylase by microorganisms, giving a synergistic impact. The newcombination provides a synergistic end result effectively decreasing orpreventing starch degradation.

Accordingly, the present disclosure relates to a biocidal compositioncomprising zinc ions (e.g., via a zinc ion source compound) and abiocide. In an embodiment, the biocide can be an oxidizing biocide, or anon-oxidizing biocide, except zinc pyrithione or1,2-benzoisothiazolin-3-one and zinc pyrithione (i.e., non-oxidizingbiocide excludes zinc pyrithione or 1,2-benzoisothiazolin-3-one and zincpyrithione for biocidal composition embodiments). Preferably, thebiocide in the biocidal composition of the present disclosure is anoxidizing biocide.

An embodiment of the present invention includes a biocidal system,biocidal combination or biocidal mixture that includes the individualcomponents of zinc ions and a biocide, which can form an in situbiocidal composition. An embodiment of the present disclosure includes abiocidal system that includes a combination of zinc ions and a biocide.In an embodiment, the biocide is an oxidizing biocide or a non-oxidizingbiocide, preferably the biocide is an oxidizing biocide. A proviso ofthe biocidal system of the invention is that the non-oxidizing biocidedoes not include zinc pyrithione or both 1,2-benzoisothiazolin-3-one andzinc pyrithione.

The present disclosure and invention further relates to a method forcontrolling starch degradation in starch-containing process waters frompulp, paper or board production, comprising treating the process waterwith a biocidal system comprising zinc ions and a biocide. In addition,the present disclosure and invention relates to the use of a biocidalsystem comprising zinc ions and a biocide, for treatment ofstarch-containing process waters from pulp, paper or board production.The biocide can be an oxidizing or non-oxidizing biocide. The biocidalsystem is used in an amount effective to decrease or prevent starchdegradation. In regard to methods for controlling starch degradationand/or treating process waters with the biocidal system, thenon-oxidizing biocide can include zinc pyrithione or both zincpyrithione and 1,2-benzoisothiazolin-3-one. It is also possible thateither zinc pyrithione or both zinc pyrithione and1,2-benzoisothiazolin-3-one are used as the biocidal system in themethods of the invention.

Preferred embodiments of the invention are described in the descriptionhereinafter, the examples, the claims and the figures.

DRAWINGS

FIG. 1 shows protection of starch from degradation using zinc andmonochloramine (MCA), wherein two contact times, 4 h and 24 h, wereused. Zinc concentration is given as mg of Zn²⁺ ions per liter and MCAconcentrations are given as mg of active chlorine per liter.

FIG. 2 shows protection of starch from degradation using zinc andchlorine dioxide (ClO₂), wherein two contact times, 4 h and 24 h, wereused. Zinc concentration is given as mg of Zn²⁺ ions per liter and ClO₂concentrations are given as mg of chlorine dioxide per liter.

FIG. 3 shows protection of starch from degradation using zinc andperformic acid (PFA), wherein two contact times, 4 h and 24 h, wereused. Zinc concentration is given as mg of Zn²⁺ ions per liter and PFAconcentrations are given as mg of PFA (active ingredient) per liter.

FIG. 4 shows protection of starch from degradation using zinc andglutaraldehyde, wherein two contact times, 4 h and 24 h, were used. Zincconcentration is given as mg of Zn²⁺ ions per liter and glutaraldehydeconcentrations are given as mg of glutaraldehyde (active substance) perliter.

It is known that Zn ions can inhibit the enzyme amylase (see, forexample: Irshad et. al. 1981: Effect of Zn²⁺ on plant a-amylases invitro. Phytochemistry. 20:2123-2126). According to the presentdisclosure Zn ions can be used in combination with a biocide, whichyields an unexpected synergistic effect in preventing or decreasing(e.g., about a 90% decrease or more, about a 80% decrease or more, abouta 70% decrease or more, about a 60% decrease or more, about a 50%decrease or more, about a 40% decrease or more, about at 30% decrease ormore, or about a 20% decrease or more, relative to a system notincluding the Zn and biocide) starch degradation. E.g., degradation caninclude breaking down the starch into smaller components, e.g., reducingthe amount of starch present by about 10% or more, about 20% or more,about 30% or more, about 40% or more, about 50% or more, about 60% ormore, about 70% or more, about 80% or more, or about 90% or more,relative to not including the Zn and biocide.

In an exemplar embodiment, the source of the Zn ions can be an inorganicor organic zinc compound, in particular an inorganic or organic zincsalt. Preferably, the zinc ion source is selected from ZnBr₂, ZnCl₂,ZnF₂, ZnI₂, ZnO, Zn(OH)₂, ZnS, ZnSe, ZnTe, Zn₃N₂, Zn₃P₂, Zn₃As₂, Zn₃Sb₂,ZnO₂, ZnH₂, ZnC₂, ZnCO₃, Zn(NO₃)₂, Zn(ClO₃)₂, ZnSO₄, Zn₃(PO₄)₂, ZnMoO₄,ZnCrO₄, Zn(AsO₂)₂, Zn(AsO₄)₂, Zn(O₂CCH₃)₂, or zinc metal, or acombination thereof. Preferably, an inorganic zinc salt is used.Preferred are the zinc salts ZnCl₂, ZnBr₂, ZnSO₄ and Zn(O₂CCH₃)₂, mostpreferably ZnCl₂ is used.

In an exemplar embodiment, the non-oxidizing biocides can includeglutaraldehyde, 2,2-dibromo-3-nitrilopropionamide (DBNPA),2-bromo-2-nitropropane-1,3-diol (Bronopol), quaternary ammoniumcompounds, carbamates, 5-chloro-2-methyl-4-isothiazolin-3-one (CM IT),2-methyl-4-isothiazolin-3-one (MIT), 1,2-dibromo-2,4-dicyanobutane,bis(trichloromethyl)sulfone, 2-bromo-2-nitrostyrene,4,5-dichloro-1,2-dithiol-3-one, 2-n-octyl-4-isothiazolin-3-one,1,2-benzisothiazolin-3-one, ortho-phthaldehyde, quaternary ammoniumcompounds (=“quats”), such as n-alkyl dimethyl benzyl ammonium chloride,didecyl dimethyl ammonium chloride (DDAC) or alkenyl dimethylethylammonium chloride, guanidines, biguanidines, pyrithiones,3-iodopropynyl-N-butylcarbamate, phosphonium salts, such as tetrakishydroxymethyl phosphonium sulfate (THPS), dazomet,2-(thiocyanomethylthio) benzothiazole, methylene bisthiocyanate (MBT),and a combination thereof. Preferred non-oxidizing biocides are selectedfrom glutaraldehyde, 2,2-dibromo-3-nitrilopropionamide (DBNPA),2-bromo-2-nitropropane-1,3-diol (Bronopol), quaternary ammoniumcompounds, carbamates, 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT) and2-methyl-4-isothiazolin-3-one (MIT). Most preferably, glutaraldehyde isused.

In an exemplar embodiment, the oxidizing biocides can include an oxidantselected from chlorine, alkali and alkaline earth hypochlorite salts,hypochlorous acid, chlorinated isocyanurates, bromine, alkali andalkaline earth hypobromite salts, hypobromous acid, bromine chloride,chlorine dioxide, ozone, hydrogen peroxide, peroxy compounds, such asperacetic acid, performic acid, percarbonate or persulfate salts,halogenated hydantoins, e.g., monohalodimethylhydantoins such asmonochlorodimethylhydantoin, or dihalodimethylhydantoins such aschlorobromodimethylhydantoin, monochloramines, monobromamines,dihaloamines, trihaloamines, or a combination thereof. The oxidant canbe combined with an optionally substituted N-hydrogen compound.Particular N-hydrogen compounds are selected from ammonium salts,ammonia, urea, hydantoin, isothiazoline-1,1-dioxide, ethanolamine,pyrrolidone, 2-pyrrolidone, ethylene urea, N-methylolurea, N-methylurea,acetylurea, pyrrole, indole, formamide, benzamide, acetamide,imidazoline, or morpholine. Other suitable N-hydrogen compounds aredisclosed in WO 2012/101051 A1. Particularly suitable oxidizing biocidescan include ammonium salts reacted with an oxidant, for example,ammonium bromide or ammonium sulfate, or any other ammonium salt, whichis reacted with an oxidant, e.g., hypochlorite, or urea reacted with anoxidant, e.g., hypochlorite. Preferred oxidizing biocides are selectedfrom monochloramine (MCA), chlorine dioxide, performic acid (PFA),peracetic acid, alkali and alkaline earth hypochlorite salts, andN-hydrogen compounds combined with an oxidant. Most preferably,monochloramine (MCA), chlorine dioxide, performic acid, or a N-hydrogencompound combined with an oxidant, e.g. urea reacted with an oxidant, isused.

It is also possible to use in the methods or the processes of thedisclosure zinc pyrithione. Zinc pyrithione contains Zn ions and is anon-oxidizing biocide. In the present disclosure zinc pyrithione can beused as a zinc salt.

Amounts or quantities are herein defined in ppm or mg/l, wherein ppm(parts per million) means the same unit as mg/l, so that those units areinterchangeably used. The amounts or quantities herein defined for thebiocides refer to the active ingredient of the biocide, except for thosehalogen-based oxidizing biocides separately mentioned, for which theamounts of biocides refer to the concentration of total active chlorine.In this case, the common scale for the oxidative power of the oxidizingbiocide is its activity compared to chlorine gas (Cl₂). Total activechlorine means the concentration of elemental chlorine that isstoichiometrically equivalent to the concentration of active halogen ina given system. Thus, for example, 100 mg/l of a commercial hypochloriteproduct with nominal sodium hypochlorite concentration of 15% (w/w),corresponding to a stoichiometric concentration of about 14.2 mg/l oftotal active chlorine (Cl₂), was added in process water. Activity ofsuch a product is always lowering in time, and when measured the addedquantity of hypochlorite product was 12 mg/l as total active chlorine(Cl₂), meaning that this hypochlorite addition had the same oxidativepower as would addition of 12 mg/l of elemental chlorine have had.

The amounts to be used for the zinc ions and the biocide depend on thestarch-containing process waters to be treated and the type of thebiocide used.

In an exemplar embodiment, the Zn source can be used in amount toprovide about 1 to 1000 ppm, in particular about 10 to 500 ppm, morepreferably about 20 to 200 ppm, more preferably about 50 to 150 ppm Zn²⁺ions in the starch-containing process water.

In a preferred embodiment, the zinc source is used in an amount toprovide about 0.1 to 1000 mg/l, in particular about 0.5 to 1000 mg/l,more preferably about 2 to 800 mg/l, zinc ions in the starch-containingwaters to be treated. Further preferred amounts are about 2 to 500 mg/l,in particular about 2 to 300 mg/l, preferably about 3 to 100 mg/l, mostpreferably 5 to 50 mg/l, zinc ions.

In an exemplar embodiment, the oxidizing biocide is preferably used inan amount to provide a concentration of about 0.1 to 100 ppm, inparticular about 0.1 to 50 ppm, more preferably about 0.1 to 15 ppm,more preferably about 0.5 to 10 ppm, based on the active compoundcontent of the oxidizing biocide in the starch-containing process water.In an embodiment where the oxidizing biocide contains chlorine (byactive compound content is understood a total active chlorine compound)of about 0.1 to 100 ppm, in particular about 0.1 to 50 ppm, morepreferably about 0.1 to 15 ppm, more preferably about 0.5 to 10 ppm inthe starch-containing process water.

In a preferred embodiment, the oxidizing biocide is used in an amount toprovide a concentration of about 0.1 to 1000 mg/l, in particular about0.5 to 500 mg/l, more preferably about 0.5 to 100 mg/l, even morepreferably about 0.7 to 50 mg/l, most preferably about 1 to 20 mg/l, ofthe active ingredient of the oxidizing biocide, in the starch-containingwaters to be treated.

In an exemplar embodiment, the non-oxidizing biocide is preferably usedin an amount of about 0.1 to 1000 ppm, preferably about 1 to 500 ppm,more preferably about 5 to 100 ppm in the starch-containing processwater.

In a preferred embodiment, the non-oxidizing biocide is used in anamount to provide a concentration of about 0.1 to 1000 mg/l, inparticular about 0.5 to 500 mg/l, more preferably about 0.5 to 200 mg/l,more preferably about 1 to 100 mg/l, most preferably about 2 to 50 mg/l,of the active ingredient of the non-oxidizing biocide, in thestarch-containing waters to be treated.

In the present disclosure ppm means weight of active compound per volumeof the process water. Process water includes the solid matter.

In an exemplar embodiment, the Zn ions and the oxidizing biocide can beused in a ratio of about 1:1 to 100:1. In a preferred embodiment of thebiocidal system, the zinc ions and the oxidizing biocide are present ina ratio of about 1:10 to 100:1, preferably about 1:5 to 20:1, morepreferably about 1:2 to 5:1, based on the weight of the components.

In an exemplar embodiment, the zinc ions and the non-oxidizing biocidecan be used in a ratio of about 1:10 to 10:1. In a preferred embodimentof the biocidal system, the zinc ions and the oxidizing biocide arepresent in a ratio of about 1:20 to 20:1, preferably about 1:10 to 10:1,more preferably about 1:5 to 5:1, based on the weight of the components.

If zinc pyrithione is used, it is preferably used in an amount of about0.1 to 1000 ppm, preferably about 1 to 500 ppm, more preferably about 5to 100 ppm, in the starch-containing process water.

The zinc ions and the biocide can be continuously, intermittently oralternately added to the starch-containing waters to be treated. Thezinc ions and the biocide can be added simultaneously or sequentially tothe waters to be treated. In case of sequential addition, the biocidecan be added prior to the addition of the zinc ions, or the zinc ionscan be added prior to the addition of the biocide. According torequirements, it is also possible to add one component continuously andthe other component intermittently.

In an exemplar embodiment, the components of the biocidal system can beadded simultaneously or sequentially to the process water. If addedsequentially, the time between the single additions should preferablynot exceed, about 180 minutes, preferably about 60 minutes, morepreferably about 30 minutes, more preferably about 20 minutes, morepreferably about 10 minutes, or more preferably about 5 minutes. In anembodiment, the Zn is added first, and in another embodiment, the Zn isadded second. In an embodiment, the components can be mixed together andadded all at once or in portions. In an embodiment, the components areadded separately all at once or in portions. In an embodiment, a portionof the Zn is added and then a portion of the biocide is added and thiscan be alternated in the same or different time frames until all of theZn and biocide are added. In an embodiment, a portion of the biocide isadded and then a portion of the Zn is added and this can be alternatedin the same or different time frames until all of the Zn and biocide areadded.

The present disclosure can be used for process waters from the pulp,paper and board producing industry, which process waters contain starch.In general, the biocidal system can be added to a position containingstarch and including components that may degrade the starch. Thebiocidal system can be added to the broke system, pulp, pulp storagetanks, to the water entering the pulper or into the pulper, waterstorage tanks, or pipe line before the broke or pulp storage tanks. Inparticular, the biocidal system can be used in pulping ofstarch-containing recycled fiber and/or in broke systems. Reduced starchconsumption would gain paper makers a significant saving in starchconsumption, reduce runnability problems and increase paper quality.

The invention also relates to the use of a biocidal system comprisingzinc ions and a biocide, for treatment of starch-containing processwaters from pulp, paper or board production. The zinc ions and thebiocide can be the same as defined above. The biocidal system can beadded to a broke system, pulp, pulp storage tanks, to the water enteringthe pulper or into the pulper, water storage tanks, or pipe line beforethe broke or pulp storage tanks.

The invention further relates to a method of inhibiting existing amylaseactivity, and/or preventing or reducing the production of new amylase bymicroorganisms in starch-containing fluid, wherein the method comprisestreating the fluid with zinc ions and a biocide. The zinc ions and thebiocide can be the same as defined above. The starch-containing fluidcan be the same as the above-defined process water from pulp, paper orboard production.

The invention is further illustrated by the following examples, whichshow preferred embodiments, without limiting the scope of protection.

EXAMPLE 1

Prevention of starch degradation was studied using an oxidizing biocide(monochloramine, MCA) and zinc. Head box stock from packaging boardmill, stored at +4° C. after collecting, was amended with 0.8 g/l cookedstarch and incubated overnight at 45° C. with 150 rpm shaking to inducethe growth of starch degrading bacteria. The stock was divided into 30ml portions and appropriate amounts of zinc (Zn²⁺ from zinc chloride)and MCA were added together with a new starch addition (400 mg/l). After4 h and 24 h incubation (+45° C., 150 rpm) the remaining starch wasquantified using iodine staining (Lugol-solution) at 590 nm. An externalstandard curve was used to convert absorbance values into starchamounts.

Table 1 below and FIG. 1 show that when no bacteria were present(sterile control) the measurable starch concentration was about 250 mg/lafter 4 h and 200 mg/l after 24 h. The rest of the starch had probablyretained onto fibers. In non-treated control most of the starch had beendegraded already in 4 h and almost all in 24 h. 10 mg/l zinc or MCAprevented most of the starch degradation for 4 h, but they did not haveany effect in 24 h. When zinc and MCA were applied together, clearlybetter result was obtained than with either of the chemicals alone.

TABLE 1 Protection of starch from degradation using zinc andmonochloramine (MCA). Two contact times, 4 and 24 h, were used. Zincconcentration is given as mg of Zn²⁺ I⁻¹ and MCA concentrations aregiven as mg of active chlorine I⁻¹. RHODEN, MELISSA KEMIRA OYJ (OFFICIALADDRESS) DIV OF 14/348,070 (221105-1935) PATENT APPLICATION Starchconcentration, mg/l Sample 4 h 24 h Sterile control 262 199 Control 44 7Zn 10 mg/l 177 8 MCA 10 mg/l 158 5 MCA 20 mg/l 189 41 MCA + Zn (10mg/l + 10 mg/l) 221 52 MCA + Zn (20 mg/l + 10 mg/l) 246 110

EXAMPLE 2

Prevention of starch degradation was studied using an oxidizing biocide(chlorine dioxide, ClO₂) and zinc. Head box stock from packaging boardmill, stored at +4° C. after collecting, was amended with 0.8 g/l cookedstarch and incubated overnight at 45° C. with 150 rpm shaking to inducethe growth of starch degrading bacteria. The stock was divided into 30ml portions and appropriate amounts of zinc (Zn²⁺ from zinc chloride)and ClO₂ were added together with a new starch addition (400 mg/l).After 4 h and 24 h incubation (+45° C., 150 rpm) the remaining starchwas quantified using iodine staining (Lugol-solution) at 590 nm. Anexternal standard curve was used to convert absorbance values intostarch amounts.

Table 2 hereinafter and FIG. 2 show that when no bacteria were present(sterile control) the measurable starch concentration was about 350 mg/lafter 4 h and 300 mg/l after 24 h. The rest of the starch had probablyretained onto fibers. In non-treated control most of the starch had beenconsumed already in 4 h and almost all in 24 h. 10 mg/l zinc or 5-20mg/l ClO₂ prevented most of the starch degradation for 4 h, but they didnot have marked effect in 24 h. When zinc and ClO₂ were appliedtogether, clearly better result was obtained than with either of thechemicals alone.

TABLE 2 Protection of starch from degradation using zinc and chlorinedioxide. Two contact times, 4 and 24 h, were used. Zinc concentration isgiven as mg of Zn²⁺ I⁻¹ and ClO₂ concentrations are given as mg ofchlorine dioxide I⁻¹. Starch concentration, mg/l Sample 4 h 24 h Sterilecontrol 361 314 Control 50 6 Zn 10 mg/l 219 28 ClO₂ 5 mg/l 128 5 ClO₂ 9mg/l 153 12 ClO₂ 14 mg/l 197 13 ClO₂ 20 mg/l 227 19 ClO₂ + Zn (5 mg/l +221 57 10 mg/l) ClO₂ + Zn (9 mg/l + 218 59 10 mg/l) ClO₂ + Zn (14 mg/l +253 84 10 mg/l) ClO₂ + Zn (20 mg/l + 264 97 10 mg/l)

EXAMPLE 3

Prevention of starch degradation was studied using an oxidizing biocide(performic acid, PFA) and zinc. Head box stock from packaging boardmill, stored at +4° C. after collecting, was amended with 0.8 g/l cookedstarch and incubated overnight at 45° C. with 150 rpm shaking to inducethe growth of starch degrading bacteria. The stock was divided into 30ml portions and appropriate amounts of zinc (Zn²⁺ from zinc chloride)and PFA were added together with a new starch addition (400 mg/l). After4 h and 24 h incubation (+45° C., 150 rpm) the remaining to starch wasquantified using iodine staining (Lugol-solution) at 590 nm. An externalstandard curve was used to convert absorbance values into starchamounts.

Table 3 hereinafter and FIG. 3 and show that when no bacteria werepresent (sterile control) the measurable starch concentration was about300 mg/l after 4 h. The rest of the starch had probably retained ontofibers. In non-treated control most of the starch had been consumedalready in 4 h and almost all in 24 h. 10 mg/l zinc or 20-120 mg/l PFAprevented most of the starch degradation for 4 h, but they did not havemarked effect in 24 h. When zinc and ClO₂ were applied together, clearlybetter result was obtained than with either of the chemicals alone.

TABLE 3 Protection of starch from degradation using zinc and performicacid (PFA). Two contact times, 4 and 24 h, were used. Zinc concentrationis given as mg of Zn²⁺ I⁻¹ and PFA concentrations are given as mg of PFA(active ingredient) I⁻¹. Starch concentration, mg/l Sample 4 h 24 hSterile control 289 0 Control 49 4 Zn 10 mg/l 181 38 PFA 3 mg/l 114 3PFA 5 mg/l 157 3 PFA 11 mg/l 208 5 PFA 16 mg/l 215 11 PFA + Zn (3 mg/l +10 182 37 mg/l) PFA + Zn (5 mg/l + 10 227 41 mg/l) PFA + Zn (11 mg/l +244 40 10 mg/l) PFA + Zn (16 mg/l + 229 175 10 mg/l)

EXAMPLE 4

Prevention of starch degradation was studied using a non-oxidizingbiocide (glutaraldehyde) and zinc. Head box stock from packaging boardmill, stored at +4° C. after collecting, was amended with 0.8 g/l cookedstarch and incubated overnight at 45° C. with 150 rpm shaking to inducethe growth of starch degrading bacteria. The stock was divided into 30ml portions and appropriate amounts of to zinc (Zn²⁺ from zinc chloride)and glutaraldehyde were added together with a new starch addition (400mg/l). After 4 h and 24 h incubation (+45° C., 150 rpm) the remainingstarch was quantified using iodine staining (Lugol-solution) at 590 nm.An external standard curve was used to convert absorbance values intostarch amounts.

Table 4 hereinafter and FIG. 4 and show that when no bacteria werepresent (sterile control) the measurable starch concentration was about300 mg/l after 4 h and 200 mg/l after 24 h. The rest of the starch hadprobably retained onto fibers. In non-treated control most of the starchhad been consumed already in 4 h and almost all in 24 h. 10 mg/l zinc or5-30 mg/l glutaraldehyde prevented some of the starch degradation for 4h, but they did not have marked effect in 24 h. When zinc andglutaraldehyde were applied together, clearly better result was obtainedthan with either of the chemicals alone.

TABLE 4 Protection of starch from degradation using zinc andglutaraldehyde. Two contact times, 4 and 24 h, were used. Zincconcentration is given as mg of Zn²⁺ I⁻¹ and glutaraldehydeconcentrations are given as mg of active substance glutaraldehyde I⁻¹.Starch concentration, mg/l Sample 4 h 24 h Sterile control 301 212Control 39 3 Zn 10 mg/l 193 21 GL 5 mg/l 85 3 GL 10 mg/l 103 5 GL 20mg/l 96 4 GL 30 mg/l 93 6 GL + Zn (5 mg/l + 10 174 42 mg/l) GL + Zn (10mg/l + 10 227 65 mg/l) GL + Zn (20 mg/l + 10 189 75 mg/l) GL + Zn (30mg/l + 10 185 89 mg/l)

The examples show that biocidal systems according to the inventionprovide superior effects in terms of preventing starch degradation instarch-containing process waters.

It should be noted that ratios, concentrations, amounts, and othernumerical data may be expressed herein in a range format. It is to beunderstood that such a range format is used for convenience and brevity,and thus, should be interpreted in a flexible manner to include not onlythe numerical values explicitly recited as the limits of the range, butalso to include all the individual numerical values or sub-rangesencompassed within that range as if each numerical value and sub-rangeis explicitly recited. To illustrate, a concentration range of “about0.1% to about 5%” should be interpreted to include not only theexplicitly recited concentration of about 0.1 wt % to about 5 wt %, butalso include individual concentrations (e.g., 1%, 2%, 3%, and 4%) andthe sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within theindicated range. In an embodiment, the term “about” can includetraditional rounding according to significant figures of the numericalvalue. In addition, the phrase “about ‘x’ to ‘y’” includes “about ‘x’ toabout ‘y’”.

It should be emphasized that the above-described embodiments are merelypossible examples of implementations, and are merely set forth for aclear understanding of the principles of this disclosure. Manyvariations and modifications may be made to the above-describedembodiment(s) of the disclosure without departing substantially from thespirit and principles of the disclosure. All such modifications andvariations are intended to be included herein within the scope of thisdisclosure and protected by the following embodiments.

Preferred embodiments of the invention are described hereinafter.

Therefore, at least the following is claimed:
 1. A biocidal systemcomprising zinc ions and a biocide, which form in situ a biocidalcomposition, wherein the biocide is selected from an oxidizing biocideor a non-oxidizing biocide, with the proviso that the non-oxidizingbiocide does not include zinc pyrithione or 1,2-benzoisothiazolin-3-oneand zinc pyrithione.
 2. The biocidal system of claim 1, wherein thebiocide is an oxidizing biocide.
 3. The biocidal system of claim 1,wherein the zinc ions are derived from an inorganic or organic zincsalt, preferably an inorganic zinc salt.
 4. The biocidal system of claim1, wherein the zinc ion source is selected from: ZnBr₂, ZnCl₂, ZnF₂,ZnI₂, ZnO, Zn(OH)₂, ZnS, ZnSe, ZnTe, Zn₃N₂, Zn₃P₂, Zn₃As₂, Zn₃Sb₂, ZnO₂,ZnH₂, ZnC₂, ZnCO₃, Zn(NO₃)₂, Zn(ClO₃)₂, ZnSO₄, Zn₃(PO₄)₂, ZnMoO₄,ZnCrO₄, Zn(AsO₂)₂, Zn(AsO₄)₂, Zn(O₂CCH₃)₂), zinc metal, and acombination thereof.
 5. The biocidal system of claim 1, wherein thebiocide is a non-oxidizing biocide and selected from: glutaraldehyde,2,2-dibromo-3-nitrilopropionamide (DBNPA),2-bromo-2-nitropropane-1,3-diol (Bronopol), quaternary ammoniumcompounds (quats), carbamates, 5-chloro-2-methyl-4-isothiazolin-3-one(CMIT), 2-methyl-4-isothiazolin-3-one (MIT),1,2-dibromo-2,4-dicyanobutane, bis(trichloromethyl)sulfone,2-bromo-2-nitrostyrene, 4,5-dichloro-1,2-dithiol-3-one,2-n-octyl-4-isothiazolin-3-one, 1,2-benzisothiazolin-3-one,ortho-phthaldehyde, guanidines, biguanidines, pyrithiones,3-iodopropynyl-N-butylcarbamate, tetrakis hydroxymethyl phosphoniumsulfate (THPS), dazomet, 2-(thiocyanomethylthio)benzothiazole, methylenebisthiocyanate (MBT), and a combination thereof.
 6. The biocidal systemof claim 1, wherein the biocide is an oxidizing biocide and selectedfrom: chlorine, alkali and alkaline earth hypochlorite salts,hypochlorous acid, chlorinated isocyanurates, bromine, alkali andalkaline earth hypobromite salts, hypobromous acid, bromine chloride,chlorine dioxide, ozone, hydrogen peroxide, peroxy compounds,halogenated hydantoins, monochloramines, monobromamines, dihaloamines,trihaloamines, an optionally substituted N-hydrogen compound combinedwith an oxidant, ammonium salts reacted with an oxidant, or acombination thereof.
 7. A method of controlling starch degradation instarch-containing process water from pulp, paper or board production,comprising: treating the process water with zinc ions and anon-oxidizing biocide.
 8. The method of claim 7, wherein the zinc ionsand the biocide are continuously, intermittently or alternately added tothe starch-containing process water.
 9. The method of claim 7, whereinthe zinc ions and the biocide are added simultaneously to thestarch-containing process water.
 10. The method of claim 7, wherein thebiocide is added prior to the addition of the zinc ions.
 11. The methodof claim 7, wherein the zinc ions are added prior to the addition of thebiocide.
 12. Use of a biocidal system comprising zinc ions and abiocide, for treatment of starch-containing process waters from pulp,paper or board production.
 13. The use according to claim 12, whereinthe zinc ions and the biocide is an oxidizing biocide.
 14. The useaccording to claim 12, wherein the biocidal system is added to the brokesystem, pulp, pulp storage tanks, to the water entering the pulper orinto the pulper, water storage tanks, or pipe line before the broke orpulp storage tanks.